In recent medical treatment, centrifugal blood pumps are increasingly used in artificial heart/lung units for extracorporeal blood circulation. Centrifugal pumps of the magnetic coupling type wherein a driving torque from an external motor is transmitted to an impeller through magnetic coupling are commonly used because the physical communication between the blood chamber of the pump and the exterior can be completely excluded and invasion of bacteria can be prevented.
The turbo-type pump disclosed in Japanese Patent Application Laid-Open No. 4-91396 (patent document 1) is described below as an example of the centrifugal blood pump. In the turbo-type pump disclosed therein, the magnetic coupling is formed by the first permanent magnet provided at one side of the impeller and the second permanent magnet opposed to the first permanent magnet through the housing. The rotor on which the second permanent magnet is mounted is rotated. Thereby the impeller is attracted toward the rotor with the impeller rotating. The impeller is spaced at a small interval from the inner surface of the housing owing to the hydrodynamic bearing effect generated between the groove for hydrodynamic bearing and the inner surface of the housing. Thus impeller rotates without contacting the housing.
In the hydrodynamic bearing pump, the fluid-feeding impeller is kept out of contact with peripheral surfaces of surrounding parts by a load-carrying capacity (load-carrying capacity is a term of a bearing and has dimension of force) generated by the groove for hydrodynamic bearing and a force resisting to the load-carrying capacity, for example, a magnetic force. Thereby hemolysis and thrombus are prevented from occurring.
The load-carrying capacity varies according to the configuration of the groove for hydrodynamic bearing. That is, the distance between the impeller and the surrounding parts varies according to the configuration of the groove for hydrodynamic bearing. Therefore the designing of the configuration of the groove for hydrodynamic bearing is important.
In the conventional groove for hydrodynamic bearing, the principal object is to increase the load-carrying capacity. Thus a logarithmic spiral groove is conventionally adopted. However, it is important to prevent the hemolysis to a high extent in addition to making the load-carrying capacity high.
It is a first object of the present invention to provide a centrifugal blood pump apparatus not of a type of magnetically levitating an impeller but allowing a rotation of the impeller without substantial contact between the impeller and a housing by utilizing a groove for hydrodynamic bearing and preventing occurrence of hemolysis to a high extent during use.
In the hydrodynamic bearing pump, the fluid-feeding impeller is kept out of contact with peripheral surfaces of surrounding parts by a load-carrying capacity (load-carrying capacity is a term of a bearing and has dimension of force) generated by the groove for hydrodynamic bearing and a force resisting to the load-carrying capacity, for example, a magnetic force. Thereby hemolysis and thrombus are prevented from occurring.
The present applicant proposed the centrifugal fluid pump apparatus as disclosed in U.S. Pat. No. 6,840,735 (patent document 2). The centrifugal fluid pump apparatus 1 has the control mechanism 6 and the pump body 5 including the pump section 2 having the impeller 21 rotating in the housing 20; the rotor 31 having a magnet 33 for attracting the impeller 21 thereto; a motor 34 for rotating the rotor 31; the electromagnet 41 for attracting the impeller 21 thereto, the sensor 42 for detecting the position of the impeller 21, and the groove 38 for hydrodynamic bearing provided on the inner surface of the housing 20. The control mechanism 6 has the position sensor output monitoring function 56, the electromagnet current monitoring function 57, and the motor current monitoring function.
Whether the sensor has a failure is determined by using the position sensor output monitoring function 56. Whether the electromagnet has a failure is determined by using by using the electromagnet current monitoring function 57. The centrifugal fluid pump apparatus 1 further includes the emergency impeller rotation function that operates when the failure detection function has detected that the sensor or the electromagnet has a failure to rotate the impeller 21 by utilizing the groove 38 for hydrodynamic bearing.
In the hydrodynamic pressure bearing pump, the impeller is kept out of contact with the housing in blood. However, in the pump apparatus disclosed in the patent document 1, it is impossible to find the position of the impeller. Thus it is impossible to check whether the impeller is rotating without contacting the inner surface of the housing with a predetermined interval kept between the impeller and the inner surface of the housing. The groove for hydrodynamic bearing of the pump apparatus disclosed in the patent document 2 is used for an emergency such as the failure of the sensor and not of the type of rotating the impeller by always using the hydrodynamic pressure generated by the groove for hydrodynamic bearing. The sensor does not measure the position of the impeller when the impeller is rotated without contacting the housing by the hydrodynamic pressure generated by the groove for hydrodynamic bearing.
It is a second object of the present invention to provide a centrifugal blood pump apparatus not of a type of magnetically levitating an impeller but allowing a rotation of the impeller without substantial contact between the impeller and a housing by utilizing a groove for hydrodynamic bearing and allowing the position of the impeller to be checked.